Fate and Transport of Zoonotic Bacterial, Viral, and - The Pork Store ...

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Fate and Transport of Zoonotic Bacterial, Viral, and Parasitic Pathogens during Swine Manure Treatment, Storage, and Land Application
farms were under fields where sprayfield application
of swine lagoon liquid was done, and up- and
downgradient from the swine lagoons (only one swine
farm had a monitoring well upgradient from the swine
lagoon). Although a significantly higher number of E.
coli were recovered from the swine farm groundwaters
compared with the crop farms, the majority of isolates
recovered from swine farm groundwaters (79%)
were from one farm that had evidence of aquifer
contamination resulting from a piezometer. When the
results from this farm were not included in the analysis,
there was no statistically significant difference in the E.
coli recoveries from the groundwater of the other swine
farm and the reference farms.
A controlled field experiment by Muirhead,
Collins, and Bremer (2006) evaluated the effect of
flow rate and ground tillage on the overland flow of
E. coli. In this experiment, runoff was simulated on a
5m down slope (slope angle was not specified) on plots
with intact, grassed soil and plots turned with a spade
and then cultivated with a rotary hoe. Tap water was
used initially to model runoff flow rates of 2, 6, and
20L/min., and E. coli levels were observed to increase
in the captured runoff with increased flow distance.
This suggested that background E. coli may contribute
several logs of bacteria/100mL runoff, especially at low
flow rates where more water infiltrates the soil matrix.
Dairy cattle manure was diluted with water to make a
liquid with an average E. coli concentration of 3.9 x 105
most probable number (MPN)/100mL (% solids of final
effluent not provided) and was applied to the plots at the
top of the slopes at the desired rate until captured runoff
represented a saturation-excess state. As expected,
low flow conditions (2L/min) and cultivated plots were
most effective at retaining E. coli in the soil matrix,
exhibiting a logarithmic trend of microbial reduction
with distance. At the low flow rate of 2L/min, a 40%
reduction in the bacterial concentrations was observed
on cultivated plots 5m from the application point. In
contrast, flow rates of 6L/min or more on intact, grassed
soil plots did not exhibit logarithmic removal of E.
coli and less than 10% of E. coli was removed at 5m. In
addition, 80% of E. coli recovered in the runoff was
transported on particles less than 20mm in diameter
rather than larger, dense particles. The generalizability
of these observations to natural conditions is dubious,
as this study represents extreme runoff conditions
because manure effluent was used to simulate overland
flow—thus eliminating the effects of microbial dilution,
extended contact time of microbes with soil, UV
radiation, desiccation, and temperature on the microbial
concentration of runoff.
This chapter has provided a brief overview of the
determinants of microbial survival and transport in
swine production facilities. The following chapters will
review the body of research investigating the fate and
transport of enteric microbes and known pathogens in
more detail and will provide the basis for the discussion
of the research gaps and future studies required
to systematically assess the risk of environmental
transport of zoonotic pathogens from the swine
production environment.